Two-stage polyphase interpolators and decimators for sample rate conversions with prime numbers

In this paper we demonstrate that it can be advantageous from a computational point of view to use a two-stage realization instead of a singlestage realization for sample rate conversions with prime numbers. One of the stages performs a conversion by a factor of two using linear-phase, or approximately linear-phase, half-band filters. The other stage changes the sample rate by the rational factor N/2 using a linear-phase FIR filter. The actual filtering can be performed at the lowest of the two sample frequencies involved. It is also possible to exploit the coefficient symmetry of the linear-phase FIR filter in the stage that changes the rate by a rational factor. The overall workload of the two-stage realization can therefore be reduced compared with the corresponding singlestage realization.